PC Power Supplies – Will It Give Me More FPS!?

[PCC-Jon]

Summary:
The lowly power supply – In today’s world, the power supply is often assumed to be a commodity item. Maybe the problem is that we, as PC enthusiasts, do not grasp the full import of a power supply. A power supply is like the heart of your PC – it pumps the juice to the various parts of the system. As computer desktop operating systems and general productivity software become more stable and reliable, the power supply can present the weakest link in a computer system. A faulty power supply can cause intermittent lockups and rebooting. In this article, we'll look at how to pick a good power supply

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Post your discussion here!

[rhawth]

I agree fully with Jon regarding the critical nature of this fundimental component. In the last year, my system has started to intermittently shut down and will not power back up for several minutes. Sometimes it will run for days while other times it will only run an hour. After some thought, I decided to replace the Emermax 460 watt PS which PCC sold me with my computer with a fresh one. I just received it and will swap out the old one for a brand new one today.

One nasty side effect from the old PS - at least I hope it was the old PS - is that twice now something has fried a SCSI card in my computer and I had to get a new card and replace the burned out card to get the computer to boot up (remember this problem Jon?). I don't know how it happens but it does. A second strange problem is that when my computer is plugged into my 650vA uninterruptable power supply (UPS) with the old PS installed, my UPS will all of a sudden start flashing alarms that something has overloaded it (i.e., demanded more power than it can deliver). When I move the computer to an unprotected power source such as the wall socket the UPS stops complaining.

Bottom line, there are some very nasty consequences arrising from a bad power supply and computer owners need to ensure they have a high quality PS of sufficient wattage to do the job. As for Enermax, I will give them a pass on this problem this time but it is the last time they will ever get some money from me if my power problems are not resolved with the installation of a brand new PS.

[TheMattrix]

Wow, that's surprising coming from Enermax. They're consitered by many to be in the top three for best computer power supplies. (The other two being PC Power & Cooling and Antec). Guess you just got a faulty PSU. :(

[KatharineLK]

I was glad to find this article. I recently decided I'd like to upgrade my video card, and I found a great deal on an ATI AIW radeon 9800pro. Installed fine, but after a short while, I started having funny problems...things were taking *forever* to load, and the hard drive was making intermittent "clinking" noises. I removed the new card and re-installed my old nvidia geforce4 mx 420 card. Everything seems pretty much back to normal- after I ran chkdsk - there were many errors.

It turns out the 300W power supply I *thought* I had was only 200W. Is this the cause of my problems? Or - I have a pretty old system: 2ghz athlon xp with 512mb ram- could it be something else with my system, even though it met all the required specs of the ATI card?

Any help greatly appreciated! Personally, I'd love to just chuck it all and buy a new computer to put my lovely new card in, but a new power supply certainly would cost less. :-)

[RocketRobin]

I was glad to find this article. I recently decided I'd like to upgrade my video card, and I found a great deal on an ATI AIW radeon 9800pro. Installed fine, but after a short while, I started having funny problems...things were taking *forever* to load, and the hard drive was making intermittent "clinking" noises. I removed the new card and re-installed my old nvidia geforce4 mx 420 card. Everything seems pretty much back to normal- after I ran chkdsk - there were many errors.

It turns out the 300W power supply I *thought* I had was only 200W. Is this the cause of my problems? Or - I have a pretty old system: 2ghz athlon xp with 512mb ram- could it be something else with my system, even though it met all the required specs of the ATI card?

Any help greatly appreciated! Personally, I'd love to just chuck it all and buy a new computer to put my lovely new card in, but a new power supply certainly would cost less. :-)

Your 200W PSU was barely sufficient for your PC, before you got the 9800 VGA. With the 9800 you increases the power loading by about 25W and that's just enough to push it over the edge.
The problem is intermittent, because the PSU voltage won't begin to sag until the power supply starts to heat up, like during a gaming session.

I suggest you replace the PSU with a 300W model, preferably one with active power factor correction.

[RocketRobin]

I prefer the scientific method.

A couple of important things to look for in a PSU (other than the mass of the decice itself) are:
- Active power factor correction. Power factor correction is essential to stable PC operation and active power factor correction can often allow uninterrupted operation when line levels drop as much as 40%.
- 12V rail output. With the advent of serial ATA devices, power consumption of 5V rails has dropped significantly, while 12V rail draw has increased as much (in Watts).

And, of course, you must ensure that your PSU's gross output is adequate for the demands you intend to put upon it.
For instance let's say you're building a high end PC with:
- A CPU, such as an AMD FX55 @ 104W (rated thermal design power), or a P4 550 @ 115W (rated thermal design power for the 3.4GHz F type).
Lets call this 110W.
- Four SATA HDDs.
These are typically rate at 25W each, but more often run at about 15W, putting the load up to 170W.
- A couple of SATA optical drives.
The typical power rating for one of these devices is also 25W, and like HDDs they usually use far less power. At 15W each, that brings us to 200W
- A couple of SLI 6800 Ultras.
At 70W each, this runs us up to 340W.
Those are the worst offenders on the power consumption list, but we also have to consider the lesser components. In this case adding roughly 10% to total yields about 375W.

The next thing to consider is PSU efficiency. Power supplies are rated at their maximum power draw and NOT their maximum power output.
The typical output of a PSU is between 65 and 75% of the rated power consumption. Two factors that affect output efficiency are:
- Internal PSU cooling (heatsinks, convection, etc.).
- The ambient temperature the PSU operates in (to allow cooling to occur).
Since we want our PSU to run efficiently, we will choose to install it in a chassis that has adequate ventilation, thus removing much latent heat born from other devices and allowing the PSU to operate near ambient temperature.
Note: fancy sculpted aluminium chassis look great, but have just about 0 airflow capacity. We eschew this type of chassis as it's a safe bet that one will not only blow up a PSU operating under a 375W load, but all of the rest of the expensive components in our fancy new PC.

The net result is 375W divided by 75% = 500W.
Since I want my PC to run quietly (without the PSU fan constantly operating at maximum speed), I must choose something in a 600W flavor.
After all nothing exceeds like excess :-D

In conclusion, the CPU will cost me an arm, the RAM will cost a leg, the RAID array will cost an arm and the PSU will cost the other leg :rofl